ANALYSIS OF POLAR CHOLESTEROL OXIDATION-PRODUCTS - EVALUATION OF A NEW METHOD INVOLVING TRANSESTERIFICATION, SOLID-PHASE EXTRACTION, AND GAS-CHROMATOGRAPHY

Monitoring cholesterol oxidation products is important in the evaluati on of the potential health risks associated with lipid oxidation. In t he present study, a method allowing quick and reliable analysis of pol ar cholesterol oxidation products was evaluated. After Soxhlet-lipid e xtraction, the fat was transesterified under mild conditions, thereby minimizing degradation and allowing determination of the free and este rified cholesterol oxides. Sample fractionation was achieved with amin opropyl solid phase extraction cartridges and a stepwise elution with hexane, hexane/methyl tert-butyl ether, and acetone to separate polar cholesterol oxides from cholesterol and other lipid products. Further analysis of the trimethylsilyl derivatives was performed by gas chroma tography with detection by flame ionization or mass spectrometry. A ph ytosterol oxide such as sitosterol alpha-epoxide (24 alpha-ethyl-5 alp ha,6 alpha-epoxycholestan-3 beta-ol) was employed for the first time a s an internal standard for the quantification of cholesterol oxides in foodstuffs of animal origin.